docs: def Harrison_Brunner_Hecker(dp, voidage, vs, rho, mu, L=1, Dt=None):
      r'''Calculates pressure drop across a packed bed of spheres using a
      correlation developed in [1]_, also shown in [2]_. Fourth most accurate
      correlation overall in the review of [2]_.
      Applies a wall correction if diameter of tube is provided.
  
      .. math::
          f_p = \left(119.8A + 4.63B\left(\frac{Re}{1-\epsilon}\right)^{5/6}
          \right)\frac{(1-\epsilon)^2}{\epsilon^3 Re}
  
      .. math::
          A = \left(1 + \pi \frac{d_p}{6(1-\epsilon)D_t}\right)^2
  
      .. math::
          B = 1 - \frac{\pi^2 d_p}{24D_t}\left(1 - \frac{0.5d_p}{D_t}\right)
  
      .. math::
          f_p = \frac{\Delta P d_p}{\rho v_s^2 L}
  
      .. math::
          Re = \frac{\rho v_s  d_p}{\mu}
  
      Parameters
      ----------
      dp : float
          Particle diameter of spheres [m]
      voidage : float
          Void fraction of bed packing [-]
      vs : float
          Superficial velocity of the fluid (volumetric flow rate/cross-sectional 
          area)[m/s]
      rho : float
          Density of the fluid [kg/m^3]
      mu : float
          Viscosity of the fluid, [Pa*s]
      L : float, optional
          Length the fluid flows in the packed bed [m]
      Dt : float, optional
          Diameter of the tube, [m]
  
      Returns
      -------
      dP : float
          Pressure drop across the bed [Pa]
  
      Notes
      -----
      Uses data from other sources only. Correlation will underestimate pressure
      drop if tube diameter is not provided. Limits are specified in [1]_ as:
      .. math::
          0.72 < Re < 7700 \\
          8.3 < d_t/d_p < 50 \\
          0.33 < \epsilon < 0.88
  
      Examples
      --------
      >>> Harrison_Brunner_Hecker(dp=8E-4, voidage=0.4, vs=1E-3, rho=1E3, mu=1E-3, Dt=1E-2)
      1255.1625662548427
  
      References
      ----------
      .. [1] KTA. KTA 3102.3 Reactor Core Design of High-Temperature Gas-Cooled
         Reactors Part 3: Loss of Pressure through Friction in Pebble Bed Cores.
         Germany, 1981.
      .. [2] Erdim, Esra, Ömer Akgiray, and İbrahim Demir. "A Revisit of Pressure
         Drop-Flow Rate Correlations for Packed Beds of Spheres." Powder
         Technology 283 (October 2015): 488-504. doi:10.1016/j.powtec.2015.06.017.
      '''
      Re = dp*rho*vs/mu
      if not Dt:
          A, B = 1, 1
      else:
          A = (1 + pi*dp/(6*(1-voidage)*Dt))**2
          B = 1 - pi**2*dp/24/Dt*(1 - dp/(2*Dt))
      fp = (119.8*A + 4.63*B*(Re/(1-voidage))**(5/6.))*(1-voidage)**2/(voidage**3*Re)
      return fp*rho*vs**2*L/dp